RF receiver having improved signal-to-noise ratio and method of operation

ABSTRACT

There is disclosed, for use in a CDMA receiver, a noise reduction circuit for improving the signal-to-noise ratio of a received CDMA signal comprising a series of chip sequences. The noise reduction circuit comprises: 1) a sampling circuit for generating an original plurality of samples of the received signal; and 2) a controller for determining a first plurality of time slots containing chip samples equal to Logic 1, and a second plurality of time slots containing chip samples equal to Logic 0. The controller generates a reconstructed plurality of samples by at least one of: a) modifying an order of a first Logic 1 chip sample and a second Logic 1 chip sample; and b) modifying an order of a first Logic 0 chip sample and a second Logic 0 chip sample.

This application is a continuation of prior U.S. patent application Ser.No. 09/606,892 filed on Jun. 29, 2000 now U.S. Pat. No. 6,683,908.

TECHNICAL FIELD OF THE INVENTION

The present invention is directed, in general, to wirelesscommunications devices and, more specifically, to an RF receiver havinga lower signal-to-noise ratio.

BACKGROUND OF THE INVENTION

Wireless communications systems, including cellular phones, pagingdevices, personal communication services (PCS) systems, and wirelessdata networks, have become ubiquitous in society. Wireless serviceproviders continually try to create new markets for wireless devices andto expand existing markets by making wireless devices and servicescheaper and more reliable. The price of end-user wireless devices, suchas cell phones, pagers, PCS systems, and wireless modems, has beendriven down to the point where these devices are affordable to nearlyeveryone and the price of a wireless device is only a small part of theend-user's total cost. To continue to attract new customers, wirelessservice providers concentrate on reducing infrastructure costs andoperating costs, and on increasing handset battery lifetime, whileimproving quality of service in order to make wireless services cheaperand better.

To maximize usage of the available bandwidth, a number of multipleaccess technologies have been implemented to allow more than onesubscriber to communicate simultaneously with each base station (BS) ina wireless system. These multiple access technologies include timedivision multiple access (TDMA), frequency division multiple access(FDMA), and code division multiple access (CDMA). These technologiesassign each system subscriber to a specific traffic channel thattransmits and receives subscriber voice/data signals via a selected timeslot, a selected frequency, a selected unique code, or a combinationthereof.

CDMA technology is used in wireless computer networks, paging (orwireless messaging) systems, and cellular telephony. In a CDMA system,mobile stations (e.g., pagers, cell phones, laptop PCs with wirelessmodems) and base stations transmit and receive data in assigned channelsthat correspond to specific unique codes. For example, a mobile stationmay receive forward channel data signals from a base station that areconvolutionally coded, formatted, interleaved, spread with a Walsh codeand a long pseudo-noise (PN) sequence. In another example, a basestation may receive reverse channel data signals from the mobile stationthat are convolutionally encoded, block interleaved, modulated by a64-ary orthogonal modulation, and spread prior to transmission by themobile station. The data symbols following interleaving may be separatedinto an in-phase (I) data stream and a quadrature (Q) data stream forQPSK modulation of an RF carrier. One such implementation is found inthe TIA IS-95 CDMA standard. Another implementation is the TIA S-2000standard. The order of the Walsh code spreading or 64-ary modulation andPN spreading does not affect the performance of the present inventiondisclosed below in the DETAILED DESCRIPTION OF THE INVENTION.

A data bit equal to Logic 1 in the convolutionally encoded symbols istransmitted as one 64-chip Walsh code and a data bit equal to Logic 0 istransmitted as the inverse of the 64-bit Walsh code, obtained as anexclusive-OR (XOR) between the data bit and the Walsh code.

In order to increase the reliability of CDMA receivers, base stationsand mobile stations frequently transmit M copies of the same signal,staggered in time, to the other device. The receiving device typicallyuses multiple receive paths, such as in a rake receiver, to capture eachof the copies. The captured copies are summed to produce a compositesignal in order to improve the signal to noise ratio. This allows thecomposite signal to be more easily de-spread and recognized by a signalcorrelator or matched filter. However, this approach requires a largenumber of components and a large circuit area. Additionally, therepeated transmission of M copies of the same signal is wasteful ofscarce bandwidth.

There is therefore a need in the art for improved CDMA systems that havean improved signal-to-noise ratio in the receiver. In particular, thereis a need for CDMA systems that do not require the transmission ofmultiple copies of a signal from a transmitter to a receiver. Moreparticularly, there is a need for an improved CDMA receiver capable ofimproving the signal-to-noise ratio of a single copy of a receivedsignal.

SUMMARY OF THE INVENTION

To address the above-discussed deficiencies of the prior art, it is aprimary object of the present invention to provide, for use in a CDMAreceiver, a noise reduction circuit for improving a signal-to-noiseratio of a received signal comprising a series of chip sequences. In anadvantageous embodiment, the noise reduction circuit comprises: 1) asampling circuit for generating an original plurality of samples of thereceived signal; and 2) a controller capable of determining a firstplurality of time slots, each of the first plurality of time slotscomprising a plurality of chip samples corresponding to Logic 1, and asecond plurality of time slots, each of the second plurality of timeslots comprising a plurality of chip samples corresponding to Logic 0,wherein the controller is capable of generating a reconstructedplurality of samples by at least one of: a) modifying an order of afirst Logic 1 chip sample and a second Logic 1 chip sample; and b)modifying an order of a first Logic 0 chip sample and a second Logic 0chip sample.

CDMA provides the foundation for the present invention since the codingand spreading sequence (i.e., chip sequence per bit) are known by boththe transmitter and receiver.

In one embodiment of the present invention, the controller adds thereconstructed plurality of samples and the original plurality of samplesto generate a composite signal having a reduced signal-to-noise ratio.

The controller uses a correlator or matched filter to de-spread thereceived signal and the composite signal. If the matched filter orcorrelator output does not indicate a signal match with the desiredcode, the controller generates a new pseudo-signal, sums it with thepreviously generated pseudo-signal sum and repeats the de-spreadingfunction. The process repeats until the correlator output indicates asignal match with a signal-to-noise ration (E_(b)/N_(o)) greater that aprescribed threshold or until the execution of a set number of cycles.This process performs coherent combination of the samples that representthe digital data signal states since the signal states are the amplitude+a (for a chip state of Logic 1) and the amplitude −a (for a chip stateof Logic 0). The noise components combine with random phase. Therefore,the larger the number of summed pseudo-signals, the smaller the noisecontribution.

According to another embodiment of the present invention, the CDMAreceiver is a receiver in a base station of a wireless network.

According to still another embodiment of the present invention, the CDMAreceiver is a receiver in a mobile station capable of communicating witha wireless network.

According to yet another embodiment of the present invention, the firstLogic 1 chip sample and the second Logic 1 chip sample are containedwithin a single chip.

According to a further embodiment of the present invention, the firstLogic 0 chip sample and the second Logic 0 chip sample are containedwithin a single chip.

According to a still further embodiment of the present invention, thefirst Logic 1 chip sample and the second Logic 1 chip sample arecontained within different chips and the first Logic 0 chip sample andthe second Logic 0 chip sample are contained within different chips.

According to a yet further embodiment of the present invention, thecontroller one of modifies the order of the first and second Logic 1chip samples and modifies the order of the first and second Logic 0 chipsamples according to one of a random process algorithm and apredetermined algorithm.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention so that those skilled in the art maybetter understand the detailed description of the invention thatfollows. Additional features and advantages of the invention will bedescribed hereinafter that form the subject of the claims of theinvention. Those skilled in the art should appreciate that they mayreadily use the conception and the specific embodiment disclosed as abasis for modifying or designing other structures for carrying out thesame purposes of the present invention. Those skilled in the art shouldalso realize that such equivalent constructions do not depart from thespirit and scope of the invention in its broadest form.

Before undertaking the DETAILED DESCRIPTION OF THE INVENTION below, itmay be advantageous to set forth definitions of certain words andphrases used throughout this patent document: the terms “include” and“comprise,” as well as derivatives thereof, mean inclusion withoutlimitation; the term “or,” is inclusive, meaning and/or; the phrases“associated with” and “associated therewith,” as well as derivativesthereof, may mean to include, be included within, interconnect with,contain, be contained within, connect to or with, couple to or with, becommunicable with, cooperate with, interleave, juxtapose, be proximateto, be bound to or with, have, have a property of, or the like; and theterm “controller” means any device, system or part thereof that controlsat least one operation, such a device may be implemented in hardware,firmware or software, or some combination of at least two of the same.It should be noted that the functionality associated with any particularcontroller may be centralized or distributed, whether locally orremotely. Definitions for certain words and phrases are providedthroughout this patent document, those of ordinary skill in the artshould understand that in many, if not most instances, such definitionsapply to prior, as well as future uses of such defined words andphrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, wherein likenumbers designate like objects, and in which:

FIG. 1 illustrates an exemplary wireless network according to oneembodiment of the present invention;

FIG. 2 illustrates exemplary portions of the receiver circuitry in abase station and a mobile station according to one embodiment of thepresent invention;

FIGS. 3A and 3B illustrate the constituent parts of an incoming noisybinary signal received by a mobile station or a base station;

FIG. 4A illustrates an original sampled signal captured by a basestation or a mobile station according to one embodiment of the presentinvention;

FIG. 4B illustrates a reconstructed pseudo-signal created in a basestation or a mobile station by reordering the digital samples in theoriginal sampled signal in FIG. 4A according to one embodiment of thepresent invention; and

FIG. 5 is a flow diagram illustrating the operation of the receivercircuitry in an exemplary base station or mobile station according toone embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 through 5, discussed below, and the various embodiments used todescribe the principles of the present invention in this patent documentare by way of illustration only and should not be construed in any wayto limit the scope of the invention. Those skilled in the art willunderstand that the principles of the present invention may beimplemented in any suitably arranged radio frequency (RF) receiver.

FIG. 1 illustrates exemplary wireless network 100 according to oneembodiment of the present invention. Wireless network 100 comprises aplurality of cell sites 121–123, each containing one of the basestations, BS 101, BS 102, or BS 103. Base stations 101–103 are operableto communicate with a plurality of mobile stations (MS) 111–114. Mobilestations 111–114 may be any suitable cellular devices, includingconventional cellular telephones, PCS handset devices, portablecomputers, metering devices, and the like.

Dotted lines show the approximate boundaries of the cell sites 121–123in which base stations 101–103 are located. The cell sites are shownapproximately circular for the purposes of illustration and explanationonly. It should be clearly understood that the cell sites may have otherirregular shapes, depending on the cell configuration selected andnatural and man-made obstructions.

In one embodiment of the present invention, BS 101, BS 102, and BS 103may comprise a base station controller (BSC) and a base transceiverstation (BTS). Base station controllers and base transceiver stationsare well known to those skilled in the art. A base station controller isa device that manages wireless communications resources, including thebase transceiver station, for specified cells within a wirelesscommunications network. A base transceiver station comprises the RFtransceivers, antennas, and other electrical equipment located in eachcell site. This equipment may include air conditioning units, heatingunits, electrical supplies, telephone line interfaces, and RFtransmitters and RF receivers. For the purpose of simplicity and clarityin explaining the operation of the present invention, the basetransceiver station in each of cells 121, 122, and 123 and the basestation controller associated with each base transceiver station arecollectively represented by BS 101, BS 102 and BS 103, respectively.

BS 101, BS 102 and BS 103 transfer voice and data signals between eachother and the public telephone system (not shown) via communicationsline 131 and mobile switching center (MSC) 140. Communications line 131may be any suitable connection means, including a T1 line, a T3 line, afiber optic link, a network backbone connection, and the like. Mobileswitching center 140 is well known to those skilled in the art. Mobileswitching center 140 is a switching device that provides services andcoordination between the subscribers in a wireless network and externalnetworks, such as the public telephone system. In some embodiments ofthe present invention, communications line 131 may be several differentdata links, where each data link couples one of BS 101, BS 102, or BS103 to MSC 140.

In the exemplary wireless network 100, MS 111 is located in cell site121 and is in communication with BS 101, MS 113 is located in cell site122 and is in communication with BS 102, and MS 114 is located in cellsite 123 and is in communication with BS 103. The MS 112 is also locatedin cell site 121, close to the edge of cell site 123. The directionarrow proximate. MS 112 indicates the movement of MS 112 towards cellsite 123. At some point, as MS 112 moves into cell site 123 and out ofcell site 121, a “handoff” will occur.

As is well know, the “handoff” procedure transfers control of a callfrom a first cell to a second cell. For example, if MS 112 is incommunication with BS 101 and senses that the signal from BS 101 isbecoming unacceptably weak, MS 112 may then switch to a BS that has astronger signal, such as the signal transmitted by BS 103. MS 112 and BS103 establish a new communication link and a signal is sent to BS 101and the public telephone network to transfer the on-going voice, data,or control signals through BS 103. The call is thereby seamlesslytransferred from BS 101 to BS 103. An “idle” handoff is a handoffbetween cells of a mobile device that is communicating in the control orpaging channel, rather than transmitting voice and/or data signals inthe regular traffic channels.

Wireless network 100 is a CDMA network in which, for example, MS 112 andBS 101 transmit and receive data in control channels and trafficchannels using unique codes, such as 64-bit Walsh codes, for example. Inaccordance with the principles of the present invention, MS 112 and BS101 do not require that the other device transmit multiple copies of asignal, as in the case of prior art CDMA systems. Alternatively, MS 112and BS 101 may require that the other device transmit a lesser number ofcopies of a signal than the prior art CDMA systems. As will be explainedbelow in greater detail, MS 112 and BS 101 are capable of capturingsamples of a single copy of an incoming signal and generating one ormore new “pseudo-signals” by reordering the samples of the originalreceived signal. The pseudo-signal(s) and the original signals may thenbe combined to produce a composite signal having an improvedsignal-to-noise ratio.

FIG. 2 illustrates exemplary portions of the receiver circuitry in basestation 101 and mobile station 112 according to one embodiment of thepresent invention. Base station 101 and mobile station 112 each compriseantenna 201, radio frequency (RF) amplifier 205, downconverter anddemodulation circuit 210, and analog-to-digital (ADC) sampling circuit215. RF amplifier 205 amplifies incoming radio frequency (RF) signalsdetected by antenna 201 to a usable level. Downconverter anddemodulation circuit 210 demodulates (downconverts) the amplified RFsignals to in-phase (I) and quadrature (Q) baseband signals. Each of theI and Q baseband signals comprises a mixture of noise signals and asequence of chip patterns corresponding to Logic 1 or Logic 0. Forexample, a Logic 1 data bit may be represented by a first chip patterncomprising a unique 64-bit Walsh code and a Logic 0 data bit may berepresented by a second chip pattern that is the inverse of the unique64-bit Walsh code. ADC sampling circuit 215 samples and digitizes each Iand Q baseband signal. ADC sampling circuit 215 stores the digitalsamples of the digital I and Q baseband signals in memory 220.

Those skilled in the art will recognize that ADC sampling circuit 215may consist of two ADC sampling circuits, one for the I baseband signaland one for the Q baseband signal. Those skilled in the art will alsorecognize that memory 220 may consist of two memory sections, one forstorage of sampled data for the I baseband signal and one for storage ofsampled data for the Q baseband signal.

Base station 101 and mobile station 112 further comprise controller 225,sample position randomizer 230, matched filter/correlator 235 (hereafter“correlator 235”), and clock 240. Controller 225, under the direction ofapplication programs stored in memory 220, controls ADC sampling circuit215, correlator 235, and sample position randomizer 230 and processestheir outputs until a match is found with the unique Logic 1 or Logic 0Walsh code. In particular, controller 225 may control the sampling rateand frequency for ADC sampling circuit 215 for each of the I and Qsignals and the matching process for correlator 235 for each of the Iand Q signals. Controller 225 also controls sample position randomizer230 when a match is not found in a particular sample sequence for the Iand Q signals. Further, controller 225 sums the outputs of sampleposition randomizer 230 with the previous sampled and processed I and Qsignals and transfers the result to correlator 235 for furtherprocessing. Thus, controller 225 produces a summed signal output for theI and Q signals which increases the desired signal level with respect tothe undesired noise level, thereby increasing the signal-to-noise ratioand increasing the probability of successfully detecting the desiredsignal.

When a Logic 1 or Logic 0 match for the unique 64-bit Walsh code is notdetected, controller 225 activates sample position randomizer 230.Sample position randomizer 230 randomly shifts samples of the Logic 1and Logic 0 Walsh code chips for the previously compared signal andtransfers this result to correlator 235 for processing. Depending uponthe amount of signal noise, sample position randomizer 230 may provideone to N variations of samples of the incoming signal.

Correlator 235 compares and correlates the samples of the incomingsignal with the unique Walsh codes for Logic 1 and Logic 0. When a matchis found, correlator 235 transfers the matched Logic 1 or Logic 0 to thede-interleaver and decoder of BS 101 and MS 112 for processing. Clock240 provides the required timing signals for the components of BS 101and MS 112, including ADC sampling circuit 215, memory 220, controller225, and correlator 235.

FIGS. 3A and 3B illustrate the constituent parts of an incoming noisybinary I or Q signal received by BS 101 or MS 112. Signal 300 in FIG. 3Arepresents the original information signal that is captured by BS 101 orMS 112. Signal 305 in FIG. 3B represents the noise signal that is mixedwith information signal 300 during transmission in the forward andreverse channels. Signal 300 depicts a sequence of chips in a Logic 1 orLogic 0 Walsh code, where the sequence of chips includes two binary 1chips having amplitudes of +a and one binary 0 chip having an amplitudeof −a. The shaded vertical lines represent sample points with the chips.Each chip occurs in a time slot having a duration T. Under idealconditions, BS 101 or MS 112 receives and matches signal 300 with itscorresponding unique Walsh code for a Logic 1 or Logic 0 bit, with noneed for further transmission or signal filtering.

However, as shown by FIG. 3B, received signals usually contain randomnoise components which are introduced between the points of transmissionand reception. Noise signal 305 is the random noise component of areceived signal, with the shaded vertical bars representing the positiveand negative values of the sampled noise components. Time period T isshown for comparison purposes with signal 300. When the samplecomponents of noise signal 305 exceed a minimum threshold level, noisesignal 305 may prevent the successful recovery of signal 300 unlessfiltering techniques according to the principles of the presentinvention are used.

FIG. 4A illustrates original sampled signal 400 captured by BS 101 or MS112 according to one embodiment of the present invention. Originalsampled signal 400 comprises positive going samples for two binary 1chips and negative going samples for two binary 0 chips from a Walshcode sequence. Each chip comprises five samples, with samples labeled Athrough U. The first binary 1 chip occurs in the first time slot ofduration T and comprises samples A through E. The second binary 1 chipoccurs in the fourth time slot of duration T and comprises samples Qthrough U. The first binary 0 chip occurs in the second time slot ofduration T and comprises samples F through J. The second binary 0 chipoccurs in the third time slot of duration T and comprises samples Kthrough P.

FIG. 4B illustrates reconstructed pseudo-signal 405 created in BS 101 orMS 112 by reordering the digital samples in original sampled signal 400according to one embodiment of the present invention. Like originalsampled signal 400, reconstructed pseudo-signal 405 comprises two binary1 chips (first and fourth time slots) and two binary 0 chips (second andthird time slots) and contains the same number of samples as originalsampled signal 400. However, the positions of the binary 1 chip sampleshave been randomly interchanged with each other. Similarly, thepositions of the binary 0 chip samples have been randomly interchangedwith each other. This is done for noise elimination purposes.

For example, samples F through P are still associated with binary 0chips, but the order has changed from the prior alphabetical order oforiginal sampled signal 400 to a random order of I, M, K, O, H, F, P, N,J, and G. Some of the re-ordered samples remain within the same timeslot and some of the re-ordered samples have moved to a different timeslot. Similarly, the sample order has changed for the binary 1 chips,with some of the re-ordered samples remaining within the same time slotand some of the re-ordered samples moving to a different time slot.Thus, reconstructed pseudo-signal 405 looks like a new sequence ofsamples from a new received signal, even though reconstructedpseudo-signal 405 is entirely derived from original sampled signal 400.Reconstructed pseudo-signal 405 may be used to recover the originalinformation signal from the received noisy signal. Thus, it isunnecessary to retransmit multiple copies of the original informationsignal.

Controller 225 and sample position randomizer 230 repeatedly re-orderthe chip samples and add the re-ordered samples to a sum of the originalsamples and previous re-ordered samples for each I and Q signal. Overmultiple iterations this causes the correlated components of theoriginal information signal to mutually add and causes the components ofthe noise signal to mutually cancel each other, since the noise signalis random and may contain both positive and negative values during eachbinary 1 chip or binary 0 chip.

FIG. 5 depicts flow diagram 500, which illustrates the operation of thereceiver circuitry in exemplary base station 101 or exemplary mobilestation 112 according to one embodiment of the present invention. Afteran incoming CDMA signal is amplified and downconverted to I and Qbaseband signals, ADC sampling circuit 215 samples the “M” incomingchips of the I and Q baseband signals at “N” samples per chip (processstep 505). The samples are stored in memory 220. In one embodiment, Mmay equal 64 for a Walsh code sequence.

Next, controller 225 uses synchronization signals from clock 240 todetermine chip time slots during which binary 1 (or Logic 1) chips occurand stores the samples from the binary 1 chips in a SLOT 1 set ofsamples in memory 220 (process step 510). Similarly, controller 225 usessynchronization signals from clock 240 to determine chip time slotsduring which binary 0 (or Logic 0) chips occur and stores the samplesfrom the binary 0 chips in a SLOT 0 set of samples in memory 220(process step 515).

Controller 225 sends a copy of the incoming signal samples to correlator235 for comparison with the required Walsh codes for Logic 1 and Logic 0(process step 520). If a match occurs, the matched signal is transferredto a de-interleaver and decoder for further processing (process steps525 and 530).

If a match does not occur, sample position randomizer 230 randomlyreorders sample values within a copy of the original SLOT 1 set and alsorandomly reorders sample values within a copy of the original SLOT 0 set(process steps 525 and 535). Next, controller 225 adds the randomlyreordered signal samples to the original signal samples, to therebyproduce a summed sample signal. Controller 225 then causes correlator235 to compare summed sample signal to the Walsh codes for Logic 1 andLogic 0 to determine if a match occurs (process step 540).

If a match occurs, correlator 235 transfers the matched signal tode-interleaver and decoder (process steps 545 and 550). If a match doesnot occur, sample position randomizer 230 again randomly reorders thesample values within a copy of the original SLOT 1 set and also randomlyreorders sample values within a copy of the original SLOT 0 set (repeatprocess step 535). Controller 225 then adds the randomly reorderedsignal samples to the previous summed signal sample to thereby produce anew summed sample signal. Thus, process steps 535, 540, and 545 repeatuntil a match occurs or for a predetermined number of iterations, inwhich case a error is returned.

The present invention improves the performance of wireless digitalcommunications systems by: (1) reducing the required E_(b)/N_(o) at theCDMA receiver and detector; (2) reducing the transmit power required bytransmitters for reliable transmission; (3) reducing the interferencecaused by multiple transmitters in the assigned spectrum; and (4)reducing the battery power required for mobile stations. It will have aparticularly beneficial effect on spectrum utilization by communicationssystems that employ code division multiple access (CDMA) techniqueswhere all transmitters use the same spectrum by reducing potentialinterference from other users.

An improved E_(b)/N_(o) at the vocoder results in reduced transmit powerat the mobile station through the reverse link power control. Similarly,an improved E_(b)/N_(o) at the mobile station detector results in lowerframe error rate and reduced transmit power at the base station throughthe forward link power control.

In an alternate embodiment of the present invention, the controllergenerates the sum of K pseudo-signals prior to performing thede-spreading function with the matched filter or correlator.

In another alternate embodiment of the present invention, the controllerplaces the sampled values in time slots in a predefined order in asample template based on a lookup table or interleaver matrix.

Although the present invention has been described in detail, thoseskilled in the art should understand that they can make various changes,substitutions and alterations herein without departing from the spiritand scope of the invention in its broadest form.

1. For use in a CDMA receiver, a noise reduction circuit for improving asignal-to-noise ratio of a received signal comprising a predeterminedsequence of chips, each of said chips having a value corresponding toLogic 0 or Logic 1, said noise reduction circuit comprising: a samplingcircuit capable of generating a first sequence of samples from saidreceived signal; and a controller capable of identifying samples in saidfirst sequence of samples corresponding to Logic 0 chips and identifyingsamples in said first sequence of samples corresponding to Logic 1chips, wherein said controller is further capable of generating a secondsequence of samples by at least one of: shifting positions within saidfirst sequence of samples of at least some of said identified samplescorresponding to Logic 0 chips, wherein each of said shifted samplescorresponding to Logic 0 chips is shifted from a first positioncorresponding to a Logic 0 chip to a second position corresponding to aLogic 0 chip; and shifting positions within said first sequence ofsamples of at least some of said identified samples corresponding toLogic 1 chips, wherein each of said shifted samples corresponding toLogic 1 chips is shifted from a first position corresponding to a Logic1 chip to a second position corresponding to a Logic 1 chip.
 2. Thenoise reduction circuit set forth in claim 1 wherein said controlleradds said first and second sequences of samples to generate a compositesignal having a reduced signal-to-noise ratio.
 3. The noise reductioncircuit set forth in claim 1 wherein said CDMA receiver is disposed in abase station of a wireless network.
 4. The noise reduction circuit setforth in claim 1 wherein said CDMA receiver is disposed in a mobilestation capable of communicating with a wireless network.
 5. The noisereduction circuit set forth in claim 1 wherein said controller shiftspositions of said at least some of said identified samples correspondingto Logic 0 chips according to one of a random process algorithm and apredetermined algorithm.
 6. The noise reduction circuit set forth inclaim 1 wherein said controller shifts positions of said at least someof said identified samples corresponding to Logic 1 chips according toone of a random process algorithm and a predetermined algorithm.
 7. ACDMA wireless network comprising a plurality of base stations, each ofsaid base stations comprising a noise reduction circuit for improving asignal-to-noise ratio of a received signal comprising a predeterminedsequence of chips, each of said chips having a value corresponding toLogic 0 or Logic 1, said noise reduction circuit comprising: a samplingcircuit capable of generating a first sequence of samples from saidreceived signal; and a controller capable of identifying samples in saidfirst sequence of samples corresponding to Logic 0 chips and identifyingsamples in said first sequence of samples corresponding to Logic 1chips, wherein said controller is further capable of generating a secondsequence of samples by at least one of: shifting positions within saidfirst sequence of samples of at least some of said identified samplescorresponding to Logic 0 chips, wherein each of said shifted samplescorresponding to Logic 0 chips is shifted from a first positioncorresponding to a Logic 0 chip to a second position corresponding to aLogic 0 chip; and shifting positions within said first sequence ofsamples of at least some of said identified samples corresponding toLogic 1 chips, wherein each of said shifted samples corresponding toLogic 1 chips is shifted from a first position corresponding to a Logic1 chip to a second position corresponding to a Logic 1 chip.
 8. The CDMAwireless network set forth in claim 7 wherein said controller adds saidfirst and second sequences of samples to generate a composite signalhaving a reduced signal-to-noise ratio.
 9. The CDMA wireless network setforth in claim 7 wherein said controller shifts positions of said atleast some of said identified samples corresponding to Logic 0 chipsaccording to one of a random process algorithm and a predeterminedalgorithm.
 10. The CDMA wireless network set forth in claim 7 whereinsaid controller shifts positions of said at least some of saididentified samples corresponding to Logic 1 chips according to one of arandom process algorithm and a predetermined algorithm.
 11. A wirelessmobile station capable of communicating with a plurality of basestations in a wireless network, said wireless mobile station comprisinga reduction circuit for improving a signal-to-noise ratio of a receivedsignal comprising a predetermined sequence of chips, each of said chipshaving a value corresponding to Logic 0 or Logic 1, said noise reductioncircuit comprising: a sampling circuit capable of generating a firstsequence of samples from said received signal; and a controller capableof identifying samples in said first sequence of samples correspondingto Logic 0 chips and identifying samples in said first sequence ofsamples corresponding to Logic 1 chips, wherein said controller isfurther capable of generating a second sequence of samples by at leastone of: shifting positions within said first sequence of samples of atleast some of said identified samples corresponding to Logic 0 chips,wherein each of said shifted samples corresponding to Logic 0 chips isshifted from a first position corresponding to a Logic 0 chip to asecond position corresponding to a Logic 0 chip; and shifting positionswithin said first sequence of samples of at least some of saididentified samples corresponding to Logic 1 chips, wherein each of saidshifted samples corresponding to Logic 1 chips is shifted from a firstposition corresponding to a Logic 1 chip to a second positioncorresponding to a Logic 1 chip.
 12. The wireless mobile station setforth in claim 11 wherein said controller adds said first and secondsequences of samples to generate a composite signal having a reducedsignal-to-noise ratio.
 13. The wireless mobile station set forth inclaim 7 wherein said controller shifts positions of said at least someof said identified samples corresponding to Logic 0 chips according toone of a random process algorithm and a predetennined algorithm.
 14. Thewireless mobile station set forth in claim 7 wherein said controllershifts positions of said at least some of said identified samplescorresponding to Logic 1 chips according to one of a random processalgorithm and a predetermined algorithm.
 15. For use in a CDMA receiver,a method for improving a signal-to-noise ratio of a received signalcomprising a predetermined sequence of chips, each of the chips having avalue corresponding to Logic 0 or Logic 1, the method comprising thesteps of: generating a first sequence of samples from the receivedsignal; and identifying samples in the first sequence of samplescorresponding to Logic 0 chips; identifying samples in the firstsequence of samples corresponding to Logic 1 chips; and generating asecond sequence of samples from the first sequence of samples by atleast one of: shifting positions within the first sequence of samples ofat least some of the identified samples corresponding to Logic 0 chips,wherein each of the shifted samples corresponding to Logic 0 chips isshifted from a first position corresponding to a Logic 0 chip to asecond position corresponding to a Logic 0 chip; and shifting positionswithin the first sequence of samples of at least some of the identifiedsamples corresponding to Logic 1 chips, wherein each of the shiftedsamples corresponding to Logic 1 chips is shifted from a first positioncorresponding to a Logic 1 chip to a second position corresponding to aLogic 1 chip.
 16. The method set forth in claim 15 further comprisingthe step of adding the first and second sequences of samples to generatea composite signal having a reduced signal-to-noise ratio.
 17. Themethod set forth in claim 15 wherein the CDMA receiver is disposed in abase station of a wireless network.
 18. The method set forth in claim 15wherein the CDMA receiver is disposed in a mobile station capable ofcommunicating with a wireless network.
 19. The method set forth in claim15 wherein the step of shifting positions of the at least some of theidentified samples corresponding to Logic 0 chips shifts the positionsaccording to one of a random process algorithm and a predeterminedalgorithm.
 20. The method set forth in claim 15 wherein the step ofshifting positions of the at least some of the identified samplescorresponding to Logic 1 chips shifts the positions according to one ofa random process algorithm and a predetermined algorithm.